Plants

I was at a Christmas party in conversation with a local engineer who, hearing I design food forests, wanted to pick my brain on apple trees. He had six trees in two rows of three, well spaced in his backyard. He was throwing out terms about the mainstream organic sprays he was using, and framed his questions expecting me to know some super organic spray, or spray regimen, that would fix his problems of pests and low vigor in general. I don’t think he expected the answer I gave: ‘What’s planted around the trees?’

We often think of the rules of spacing as rules for keeping other plants away from each other. In practice I find the lines blur between species, and enters a much more broad science: it’s what should be included near the plant, as well as what shouldn’t. Between these two aspects, you make or break the majority of fruit tree problems.

The lines often blur between species because, let’s face it, plants don’t grow in a vacuum and always have something growing up against them. In this guy’s case, his trees were planted right into his lawn. They were in competition with the grass.

Looking at their history, grass and trees are in most cases nemesis of one another. Trees make forest; but grass needs open space. The setting in most yards of trees with grass between is quite artificial, and only exists because we keep the grass mowed. In any other situation, trees would take over.

The prairies are the kingdom of grass, and these occured because of rain shadows, or areas where circumstances such as the Rocky Mountain range messed with the winds that carry rain, creating droughts in one part of the year, and near flooding in another. Trees don’t like that, because most have relatively shallow roots, as much as 80 percent residing in the top three feet of soil depending on the kind and its conditions; but prairie plants, such as the grasses, and Nitrogen fixers like Senna hebecarpa, put roots down unusually deep, so reach the water table whether rain comes or not.

An experiment showing the root growth of Red Delicious apple tree two years after planting.

Have you ever wondered as you pass woods how the trees survive so close? If you were planting an oak tree in your yard that would someday reach a hundred foot tall, can you imagine the spacing recommendations? They would be over fifty feet apart. Most yards couldn’t fit more than one tree. But in the woods they stand on top of each other, growing for hundreds of years, happy, and healthy.

Studies have shown that trees can grow their roots deep into the ground, but prefer to keep their roots higher in the soil if possible. There is more organic matter, hence nutrients and water, in this layer. If there isn’t, trees will try to put in the work to grow deeper. This is a lot more work, and certainly isn’t their first choice.

What trees really prefer is building networks in which they share and preserve resources. For instance, trees have what is called hydraulic redistibution, which is a fancy term for moving water not only up for their own use, but back down into the soil for storage, and horizontally to other plants. Peter Wholleben, in his book The Hidden Life of Trees recalls his surprise when he found a ring of roots from a beech tree that must have been cut down well over a century beforehand, but still had green, living roots showing above ground. It had no leaves, and the stump was gone. As he explained, citing various studies, the living trees around this ancient (should be dead) tree were feeding it sugars made in their leaves, keeping it alive. Likely, they got some kind of kickback from the extended root system because it allowed them access to more resources.

This is in ancient, established forests, so conditions aren’t quite the same for our young transplants. We can get some similar effects by growing fruit trees in more open settings, or riparian zones. These are zones similar to fencerows and overgrown fields where grasses are just converting to trees. These zones are iconically untidy and wild; but skillful gardeners know the elements of these zones, like clay in a potters hand, have the best potential to form the most beautiful, lush gardens.

Riparian zones have many layers, with notably high numbers of low growing herbaceous and woody shrubs, many of which are nitrogen fixers. The quickest way to simulate this ecology is making ‘guilds’ of plants right around your fruit trees. Here is my manual of bed building for info on quickly clearing grass without tillage. Plan on expanding these plantings every year until the beds around your trees meet. If the tree is older, and larger, the bed should extend at least a couple feet beyond its drip line.

Any guild should include at least 2 woody nitrogen fixing plants, about 5 plants that do not fix nitrogen but can be cut for mulch, such as comfrey, or a groundcover of something like mint, then several fruiting shrubs like raspberry or honeyberry, and some perennial vegetables.

This is the best method if you already have fruit trees in the ground, like our engineer friend. If you’re just planning your food forest, Robert Hart, the father of the northern food forests, recommended planting full size or standard fruit trees at recommended spacing for their size, in rows like any orchard, but then semi standard or medium trees, then dwarf trees, then shrubs, then herbaceous plants, then vines to climb and fill in the cracks between them.

I’d recommend mulching as much as you can, and planting that area with a complete planting like this. The space should be completly filled with plants, and will establish faster with less work overall.

This system gives quite attractive results that are increasingly less cost and labor than serial applications of even organic, clay-based sprays, pyrethrums and neems, let alone harsher chemicals. There is work later on, but this is of course debatable, because its mostly harvests of fruit. Sounds like pleasant work to me.

This article was originally published on Mortal Tree on 24th February 2017.

About the author: Luke Simon is garden manager for Simon Certified Organic Family Farm, and on his own time a permanent edible landscape designer in Ohio, United States. He is the author of PASSIVE Gardening and Mastering the Growing Edge. Follow him on his blog, Mortal Tree, and his Instagram @mortal_tree.

A study by UK scientists has shown that tomato plants infected with a virus are more attractive to bumblebees than healthy plants. Why would a plant virus want to change the behaviour of bumblebees?

The virus in question – cucumber mosaic virus (CMV) – can infect many different species of plant including tomatoes and a model plant called Arabidopsis thaliana. In tomatoes it causes many symptoms including yellowing, mottling, leaf distortion and can reduce the yield of seeds. As a result there is pressure for populations of plants to evolve better defences against the virus. Since CMV can only multiply within plant cells you might expect that, over time, CMV might become less common, but this doesn’t appear to be the case. One way the virus might be able to combat this problem is to compensate for the decrease in seed production in infected plants by encouraging pollinators, such as bumblebees, to visit the flowers.

Bumblebees fertilise tomato flowers by a process called buzz pollination, in which sounds produced by the bees shake the flowers to release pollen. Although tomato flowers can fertilise themselves without help from the bumblebees, buzz pollination makes the process more efficient and also leads to the transfer of pollen between flowers. Volatile compounds (molecules that easily become gases) released from the plants may help to guide the bees to the flowers. CMV infection can change the mix of volatile compounds that plants produce, but it was not clear whether this changes the behaviour of the bees.

Simon Groen, Sanjie Jiang, Alex Murphy, Nik Cunniffe et al. found that the bees are more attracted to the volatiles produced by CMV-infected tomato plants than those produced by healthy, uninfected plants. In the absence of buzz pollination, CMV-infected plants produce fewer seeds than healthy plants. However, mathematical modeling indicates that, in the “wild”, the bee’s preference for virus-infected flowers may help to compensate for this so that CMV-infected plants may produce more seeds than uninfected plants. Further experiments in A. thaliana suggest that molecules of micro ribonucleic acid (or miRNA for short) produced by the plants might regulate the mix of volatiles that plants produce.

These findings suggest that in some environments it may be in a virus’ interest to help its host plant by making the plant more attractive to bumblebees or other pollinators. Bumblebees are important pollinators for many crop plants so these findings may help us to develop new ways to increase crop yields in the future.

Blackberries change colour from red to black as they ripen. Image by Thomas’ pics (CC BY 2.0 via Flickr)

In England at this time of year, the hedgerows along country lanes are full of delicious fruits called blackberries. Just last week I spent an enjoyable afternoon with friends gorging on blackberries along the route of an old railway line in Norwich (now a footpath and cycleway). The berries are a good source of vitamin C and antioxidants, and are commonly used in desserts and preserves. Although I love collecting and eating blackberries, I have a bit of a love-hate relationship with the plant that produces them, the bramble (Rubus fruticosus agg.).

Rubus fruticosus agg. isn’t a single species, but instead is a group (or aggregate; agg) of around 200-300 very similar species of shrub in the rose family that are very hard to tell apart (1). Like roses, brambles are covered in sharp thorns that help to protect the plant from herbivores (and humans). The thorns also help to make brambles a safe haven for many small birds and other wildlife.

Brambles grow wild across most of Europe and in the UK they can thrive in most environments (1). The white or pinkish flowers are self-fertile and can still produce seeds even in the absence of fertilization (a process called apomixis) to produce an army of clone plants (2). Furthermore, brambles can produce suckers – new shoots from buds in the roots – which helps them rapidly cover an area of ground. As a result, brambles are often among the first plants to colonise abandoned plots of land. This is great for wildlife and the casual blackberry picker, but it’s not so helpful if you are trying to work on said piece of abandoned land…

When some friends and I took on an allotment this year, our plot had been neglected for a while and contained quite a lot of brambles. We removed a lot of the plants but have left some to be our own personal blackberry patch. Removing brambles is not a fun business as the thorns can cut through clothes (and gardening gloves). For several weeks in the spring my arms and legs were covered in scratches and I often found bramble thorns impaled in my fingers. If you don’t manage to completely remove the whole root, the bramble is quite capable of growing a fresh shoot so we’ve had a few cheeky brambles reappearing in the vegetable beds.

Despite my moaning about brambles I must say that the blackberry crop from the allotment has been great. It is kind of ironic that our most successful crop this year is something we weren’t deliberately growing. All in all, if I had to summarize my relationship with the bramble at the moment, I would say: “it’s complicated”.

While giving my undergraduate class a tour of a botanic garden, a university professor said that “we should only eat the parts of a plant that the plant wants us to eat”. He was referring to the fruit, which many plants encourage animals to eat in order to spread their seeds in the environment (though not all fruits are edible). I don’t think he meant us to take his advice literally, but it is sensible to eat plants with caution. Alongside famous poisons including belladonna and hemlock, plants produce a variety of other molecules that aim to deter animals from eating them. Some of these molecules – such as ricin, which is produced by the castor oil plant – are so poisonous that tiny quantities can kill you. Others, like caffeine or the anti-malaria drug quinine, have less dramatic effects on the human body that we may find desirable or useful.

I recently visited The Alnwick Garden in north-east England, which has a special garden dedicated to educating visitors about the potential dangers of plants. In fact, some of the plants on display in the Poison Garden are so dangerous that visitors can only enter as part of a guided tour. I really enjoyed the tour and if you are ever in the area I recommend you pay the garden a visit.

The tour included some well-known poisonous plants, but the main message I took home from the tour was that many common garden plants are also potentially dangerous if they touch your skin or you accidently eat them. Below are a few examples of common plants that aren’t as benign as they might first seem:

Rhubarb (Rheum x hybridium)

While the pink fleshy stalks of the rhubarb plant are safe to eat and are commonly used in desserts, the leaves are highly toxic (1). This is thought to be due to the presence of high levels of oxalic acid, which can interfere with chemical reactions in the body by combining with calcium and other metals.

Common ivy (Hedera helix)

This rapidly growing vine is a haven for wildlife and attracts at least 70 species of nectar-feeding insects in its native range of Europe and Western Asia (2). Contact with ivy can cause an allergic skin reaction in some people, due to a natural pesticide in the leaves called falcarinol (3). Regardless of whether you are allergic to ivy or not, you should avoid eating this plant because its leaves contain saponins, which can cause vomiting, convulsions and even death.

Common nettle (Urtica dioica)

Children quickly learn that contact with common nettles results in a painful stinging sensation and skin inflammation. This is due to a cocktail of molecules including histamine, serotonin and oxalic acid, which is released from hairs on the surface of the leaves. For more information check out this cool infographic by Compound Interest.

Common laburnum (Laburnum anagyroides)

All parts of this small tree are poisonous, due to the presence of a molecule called cytisine, which has a similar structure to nicotine and has similar effects on the body. Laburnam is a member of the pea family and cases of laburnam poisoning are often caused by individuals mistaking laburnum seeds for peas and eating them (4). Mild cases may cause nausea and vomiting, but laburnum poisoning can also lead to insomnia, convulsions and coma.

These are just a few examples of common garden plants that can be harmful to humans and other animals. Fortunately, you can protect yourself against these and other poisonous plants by taking simple precautions, such as wearing gloves while gardening and carefully identifying edible plants when foraging.

Author’s note: Sorry for the long silence on this blog. My life has been quite chaotic in the last few months due to several events (expected/not expected, good/bad) and so the blog has had to take a back seat. Things are calming down a bit now so I’m hoping to get back into posting regularly, probably about twice a month. As ever, I’m always keen to receive guest posts so if you are interested in writing for Plant Scientist, please do get in touch.

In Lab Girl, scientist Hope Jahren has cleverly weaves a memoir of her own life with passages about the lives of plants, her scientific passion. From her childhood in a small town in Minnesota to her current position as a Professor at the University of Hawai’i, she gives a candid account that includes some of the adventures, funny incidents, obstacles, and shifts in her scientific thinking that happened along the way. The book is a fascinating window into the life of a gifted, passionate, yet (reassuringly) human scientist. If you haven’t read it yet, then I highly recommend you get your hands on a copy.

If you aren’t convinced by my mini-review, then I suggest you check out this longer review from the NY times.

Last week this blog celebrated its third birthday. In that time I have gone from being a research scientist to working as an editor for a scientific journal and so the involvement of plants in my life has changed somewhat. Working with plants was one of my favourite parts of my old role in research and so its perhaps not surprising that I now do quite a bit of gardening in my spare time.

Until about a year ago, the extent of my gardening experience was a few herbs in pots outside and a bunch of low-maintenance houseplants. I wasn’t always very good at looking after these plants, so branching out to a whole, albeit small, garden has all been a bit of an experiment!

I’m happy to say that my gardening experiment has overall been pretty successful so far. I’ve managed to grow some edible vegetables and my garden looks much tidier and more colourful than it did when I moved in. Most importantly, now that I have an office job, I’ve really enjoyed having a good excuse to spend lots of my leisure time outside. However, my first year in the garden hasn’t been completely plain sailing as I ran into a few problems and disasters along the way. Here are the most useful lessons I have learnt along the way:

Be on the alert for pests – they WILL find your favourite plants. Last year, slugs and snails attacked my salad leaves and destroyed the marigolds I was growing. I tried out a few different methods to deter them from eating the rest of my crops and eventually settled on copper tape. Slugs and snails don’t like crawling over copper and so I could use the tape to make a pretty good barrier to defend a lot of my vegetable crops. Unfortunately, the same cannot be said for my nasturtiums (Tropaeolum majus), which became infested with hundreds of blackflies (a type of aphid) and withered and died soon after.

That plant support or structure might look tidy, but will it withstand the weather? I must admit that the first few structures I built to support plants were not all as robust as they should have been because I didn’t really appreciate how windy it would be in my garden. The canes holding up my tomatoes were blown over on several occasions, and the netting structure protecting my cabbages nearly flew away in a winter gale.

When digging in an overgrown patch of ground, keep an eye out for plants you might want to keep. Last year, I got a good crop of potatoes from the handful of tubers left in the vegetable patch by the previous occupants of the house. And just this week I discovered some parsnips growing amongst the grass of the overgrown allotment I’ve recently taken on with some friends. Being fairly hopeless at plant identification, I didn’t know what potato or parsnip plants looked like until I stumbled into them.

Work out what types of plants you like to grow and then grow them. I like to feel “productive” when I’m gardening, so I can spend hours tending to my vegetable patch and then forget to water my houseplants. As a result, I’ve tried to fill as much of my garden with fruit and vegetables as possible, and then used low-maintenance decorative plants to fill in the gaps and really shaded areas.

My main gardening project for this year is to work on an allotment with my friends. The plot hasn’t been cultivated in a few years so was pretty overgrown, but since we took on the tenancy a couple of months ago, we have managed to clear some parts of it and plant some soft fruit crops. Watch this space.

An AM fungus (yellow) contacts the surface of a plant root. The nuclei of the plant cells are visible as blue spots. Image adapted from ref 3. Credit: Andrea Genre and Mara Novero (CC BY 3.0).

Plants need nutrients to be able to grow. Unfortunately, many of these nutrients can be scarce in the soil and therefore hard to get hold of. To get around this problem, most plants are able to form friendly relationships – known as symbioses – with soil microbes that can provide them with certain nutrients in exchange for sugars.

Today, around 80% of land plants form symbioses with a group of fungi known as arbuscular mycorrhizal (AM) fungi (1). Fossil evidence suggests that this symbiosis first emerged around 450 million years ago. This is around the same time that plants first started to colonise land. The transition from water to the dry and harsh environments on land would have presented many challenges to the early land plants, for example, how to avoid losing too much water. Another challenge would have been how to access essential nutrients that their ancestor (a type of green algae) would have gained directly from the water.

The liverworts, hornworts and mosses are thought to be the earliest groups of land plants (2). Since the AM symbiosis is widespread in these groups, it has been suggested that this symbiosis is one of the innovations that helped these primitive plants to survive on land.

Previous studies have identified many plant genes that are needed for AM symbiosis in legumes and other land plants. These genes can be split into two main groups: some are in a signalling pathway needed for the plant and fungus to communicate with each other, and others are activated later to allow the fungus to infect into the roots of the plant. Recently, Pierre-Marc Delaux and colleagues used a technique called phylogenetics to analyse genetic material from many different algae, liverworts, hornworts and mosses with the aim of finding out when the AM symbiosis genes first appeared (2).

Delaux et al. show that these plant genes emerged in stages, starting from before earliest plants colonised land. The signalling pathway genes appeared first, and are present in the algae that are thought to be the closest relatives of land plants, the Charophytes (2). On the other hand, the infection genes appear to be missing from the algae, but are present in the liverworts, hornworts and mosses.

These findings suggest that the algal ancestors of land plants were pre-adapted to interact with fungi. Currently, there is no evidence to suggest that the Charophytes are able to form AM symbioses themselves. Therefore, it is possible the signalling pathway evolved to allow algae to interact with other microbes and was later altered to allow the early land plants to interact with AM fungi.